Replace OperationQueue with Custom Dispatcher

[sureshjoshi]

The Operation Queue is neat, but a giant pain in the ass to extend - with all of its quirks.

Blueteeth has a super simple Dispatcher at around 40 lines of code, and it'll work just as well as SwiftyTeeth needs for a SerialDispatcher

[sureshjoshi]

Just discovered some more race conditions using a piece of hardware that disconnects immediately after receiving a TX message - basically, the existing message in the queue doesn't finish up, so just loiters and blocks the queue (even after cancellation).

Definitely need a better queue system.